The proposed research seeks to establish unambiguously the pathway of hydrogen transfer in the interconversion of UDP-glucose and UDP-galactose catalyzed by UDP-galactose-4-epimerase. The role of enzyme-bound pyridine nucleotide, the role of the enzyme, and the nature(s) of substrate-derived intermediate(s) are to be investigated. It is also proposed to study the mechanistic relationship between electron transfer and group transfer in the reactions catalyzed by pyruvate dehydrogenase complex. BIBLIOGRAPHIC REFERENCES: Esherichia coli Pyruvate Dehydrogenase Complex: Improved Purification and the FAD Content. D. C. Speckhard and P. A. Frey (1975) Biochem. Biophys. Res. Communs. 62, 614-620. UDP-Galactose-4-Epimerase: Uridine Monophosphate-Dependent Reduction by alpha-and beta-D-Glucose. U. G. Kang, L. D. Nolan, and P. A. Frey (1975) J. Biol. Chem. 250, 7099-7105.